Jackie Speier smiles after voting in a special election in San Mateo, Calif., Tuesday, April 8, 2008. Speier, who as a congressional aide nearly 30 years ago was shot and left for dead on a Guyana airstrip, is seeking to win the House seat once held by her former boss. A former California state lawmaker, Speier was the favorite to win a special election to fill the House seat left vacant by the death of Democratic Rep. Tom Lantos. (AP Photo/Paul Sakuma)

Photo: Paul Sakuma, AP

Jackie Speier smiles after voting in a special election in San...

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Federal investigators examine a 40-foot section of pipeline on Glenview Drive in San Bruno, in the area where eight people were killed and 38 homes destroyed.

A few hours before a Pacific Gas and Electric Co. natural gas pipeline ruptured in a San Bruno neighborhood, killing seven people, the utility had a problem with an important piece of equipment at the Milpitas operations terminal where the pipeline originated, federal investigators said Monday.

The National Transportation Safety Board, which is investigating the Sept. 9 blast, said PG&E crews had been working in the Milpitas terminal on replacing an uninterruptible power supply system, or UPS, which is designed to make sure that electricity remains constant in the event of a blackout.

"At some point the UPS failed," said Peter Knudson, a spokesman for the safety board. "This is one of the areas we are looking at - whether the failure of the UPS at the terminal played a role in the accident."

Knudson spoke after Rep. Jackie Speier, D-Hillsborough, mentioned the equipment failure at a news conference at the blast site. Speier said she was concerned that a loss of electricity, and the steps PG&E took to recover from it, may have affected the utility's ability to regulate the pressure in the pipeline.

Speier, who represents the San Bruno neighborhood and has been briefed by safety board officials, said that at the time the pipeline failed it was running at a pressure of 386 pounds per square inch. PG&E has said it normally operated the line at a maximum of 375 pounds per square inch.

At the site of the blast, which opened up a 67-foot-long crater, the pipeline was 30 inches in diameter and roughly four feet underground.

PG&E representatives said Monday that they were working to gather more information about the failure of the uninterruptible power supply.

Bob Bea, an engineering professor at UC Berkeley, said such a failure could have affected PG&E's ability to monitor and regulate pressure in the 46-mile pipeline, which runs from Milpitas to San Francisco. But he said an additional 11 pounds of pressure per square inch, by itself, "shouldn't be enough to cause trouble."

The revelation, though, may explain why the state Public Utilities Commission, which is also investigating the disaster, asked PG&E about work it had been doing at the Milpitas terminal before the explosion.

The federal safety board has said it is exploring many possible causes of the blast, including corrosion in the pipeline, which was installed in 1956.

Speier said a "perfect storm" of factors might have led to the blast that injured more than 50 people and destroyed 37 homes.

Speier called her news conference to talk about legislation she has drafted that would require pipelines running though earthquake zones and densely populated areas to have automatic or remotely operated shut-off valves.

The gas jet that fed the San Bruno inferno leaked from the transmission pipeline for nearly two hours while PG&E workers drove to manually operated shut-off valves and closed the devices.

Speier's legislation also would force pipeline operators to contact all property owners within 2,000 feet of a natural gas transmission line and inform them of their proximity to the line.